1. Field of the Invention
The present invention is in the field of method and apparatus for powered operation of a gate. More particularly, the present invention relates to a power-drive apparatus (i.e., a gate operator) for controllably moving a gate between opened and closed positions, and which has safety features seeking both to prevent entrapment of an object or person in the gate, and also to quickly release such an entrapment should it occur. When an actual or impending blockage or obstruction of the gate occurs, the gate is stopped, backed up a short distance, and stopped again. Then the gate is released from the power drive apparatus allowing it to be moved manually. Thus, a person or animal may free themselves from entanglement in the gate, or may be freed by a bystander, for example. The safety gate operator also has features which reduce or eliminate dithering of the gate near its fully opened position in response to certain high traffic flow conditions.
2. Related Technology
It is conventional to move gates, such as those which control access to a parking lot, to a gated community, to private land, or to a garage, for example, by means of a power-drive unit which moves the gate between fully opened and fully closed positions. In this sense, the term "gate" is used generically, and includes those structures perhaps more commonly referred to as "doors," such as overhead garage doors. Thus, a gate itself may be of any one of several alternative configurations. For example, a gate may slide or roll on wheels to move horizontally along a guide way (a "slide" gate), or may swing as a single piece about a vertical hinge axis (a "swing" gate), or about a horizontal hinge axis (an "overhead" gate), or the gate may roll in sections along a vertically extending track (which track may also include a horizontal section) to open and close (a sectional overhead gate or door).
Ordinarily, the power-drive unit for such gates includes an electric motor with a speed reduction drive train coupled to the gate to effect its movement between the fully opened and fully closed positions. In some cases the speed reduction drive train is implemented mechanically, and in other cases hydraulics are used for this purpose. The limits of movement of the gate which establish the fully opened and fully closed positions are generally set using conventional limit switches associated with the power drive mechanism. Some gate operators simply stall the drive mechanism by driving the gate forcefully against physical limit stops for the movement of the gate. In these cases, a motor current sensor is used to detect the stalled condition and to shut off the drive motor.
Several different safety mechanisms and devices are known and used in various combinations with conventional gate operators, and are intended to facilitate the operation of the gate, to prevent or reduce the impact of the gate against an object that gets in its way, and to also prevent entrapment of an object, animal, or person in the gate. For example, some conventional gate operators employ a light beam and detector (i.e., a photosensor) to sense when an object or person obstructs movement of the gate so as to produce a safety signal. Other gate operators use a "loop detector" which is a buried inductive coil placed in the road way leading to or from a gate opening to produce a safety signal informing the control system of the gate operator when a vehicle has approached or is departing from the gate opening. The control system will include a logic unit effecting a decision algorithm so that a vehicle which is stopped in the gate opening will be known to the gate operator and the gate will not be closed on this vehicle.
Still other gate operators have an "edge sensor" installed on the gate itself to detect when the gate makes contact with an object or person during its movement between its fully opened and fully closed positions, and to consequently produce a safety signal.
Alternatively, a gate operator may employ a motor current sensor to detect approximately when the gate is at its limit positions. When the gate is not proximate to its limit positions, and is thus intermediate of the limit positions in its opening or closing movements, then in the event that an object is encountered and either resists the gate movement sufficiently to cause the drive motor to draw a current above a certain value, or to stop the gate movement by stalling the drive motor entirely (thus, also causing a high motor current), then the gate movement is stopped and then reversed. This causes the gate to disengage from and move away from what ever it has contacted to cause its motion to be resisted or stopped. Some gate operators stop and reverse to their opposite limit of movement. Other gate operators, if they are moving in a closing direction will stop and reverse to their fully opened position. However, if they are moving the gate in an opening direction and such a "high motor current" event takes place, they simply stop the gate and reverse it a short distance only to clear the obstruction. These gate operators do not drive the gate completely to its closed position in such cases. However, in each case the gate remains connected to its drive train. Thus, with conventional gate operators, after an obstruction is encountered and the gate stops, it will not be possible to move the gate manually in order to free an entangled animal or child, for example.
Still other safety devices for gate operators are known and are used in various ways. For example, an ultrasonic transducer can be used to beam sound waves into the area of a gate opening so as to be used as a form of "sonar" to detect objects and people in this gate opening.
In view of the above, it is clear that conventional gate operators have been known for some time which include provisions to detect an object or person in the path of the gate, and to stop the gate in response to this detection. Further, some gate operators have been known which automatically stop and then reverse the direction of gate movement when an object or person is detected or encountered by the gate so as to free any entrapment by the gate which may have occurred. One disadvantage of this method of preventing or freeing an entrapment in the gate is that a person or animal, for example, may have become entangled in the gate, and will then possibly be dragged or injured as the gate is moved in its reversed direction.
Further, experience has shown that children playing or hiding near a gateway present a great risk of entrapment or entanglement. A child or a pet animal, for example, may become entrapped by the gate either when it is opening or closing. In either case, should a child or animal become entrapped and entangled in the gate, a gate operator which merely stops the gate and then reverses its direction to the other limit of gate movement can result in the child or animal possibly being injured by the initial entrapment, and then possibly being dragged and additionally injured as the gate moves in the reverse direction to the limit of its movement. Even those conventional gate operators which stop the gate, and which possibly back the gate away from an obstruction or blockage only a short distance before stopping again, maintain the gate connected to its drive train so that the gate may not be easily moved by an animal, child or bystander, to free the obstruction from the gate.
Another aspect of conventional gate operators which is a disadvantage is their tendency to repeatedly close partially from their fully opened position during periods of continual traffic flow through the gate opening, which traffic flow happens to have an interval between vehicles which is approximately matching the time-out interval of a fully-opened-pause timer of the gate operator. That is, with conventional gate operators, after a particular vehicle has passed through the gate opening, a timer included in the control system of the gate operator times out, and the gate then starts to close. This pause at the fully opened position of the gate may be referred to as a "fully-opened-pause".
If it happens that the interval between vehicles of traffic through the gate is very frequent the safety devices, such as the loop detectors buried in the drive way extending through the gate way, will keep the fully-opened-pause timer in a reset condition so that is does not time out and so that the gate does not begin to close after each vehicle. However, should the frequency of traffic flow through the gateway (i.e., the interval between vehicles) about match the time interval of the fully-opened-pause timer, then the gate will dither.
That is, the gate will start to close, and will stop and re-open again for the next vehicle. Ordinarily, concerns for preventing unauthorized vehicles from passing through the gate opening will dictate that the gate pauses only momentarily at its fully opened position. Consequently, during periods of continual traffic flow with a frequency of passage through the gate opening generally matching the interval of the fully-opened-pause timer, another vehicle may approach the gate while it is closing after its fully-opened-pause, and this vehicle will request passage through the gate opening. In this case, the gate will stop its closing movement and then re-open. When the gate reaches its fully opened position the fully-opened-pause timer will start again (i.e., reset) and will again start the gate closed when it times out. With such a frequency of continual vehicle traffic, however, the gate may again not reach its closed position before it is requested to open again. Under such circumstances, the gate can appear to be in nearly constant motion, stopping only momentarily at its fully opened position before then starting closed, only to stop and reopen in order to allow passage of the next vehicle before pausing and starting closed again.
Understandably, this dithering motion of a gate near its fully opened position is wearing on the gate operator. Further, it actually and undesirably slows down vehicular traffic flow through the gate opening because drivers are usually not willing to pass by a closing gate, and some drivers will stop their vehicle and wait until the gate stops and begins to open again before passing through the gate opening. The result of this delay of traffic actually contributes to the lengthening of the time period during which frequent traffic is passing through the gate opening. Still further, in view of the discussion above about the risk of children and animals being near a gate and possibly being entangled in the gate while it is moving, it is apparent the such dithering by a gate is highly undesirable. That is, a dithering gate spends a much greater time in motion than is actually necessary, and this motion presents a risk to children, animals, and others as described above.